Riser tensioner

ABSTRACT

A riser tensioner that tensions a riser extending to the seabed from a drilling ship which drills for submarine resources such as oil. The riser tensioner is disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and includes a plurality of cylinders. The riser tensioner further includes: an injection nozzle for injecting water to a surface of a piston rod exposed from each of the cylinders; and a scraper unit which removes salt or seawater from the surface of the piston rod by scrapping the surface of the piston rod to prevent salt from accumulating on the surface of the piston rod.

BACKGROUND

1. Technical Field

The present disclosure relates to a riser tensioner. More particularly, the present disclosure relates to a riser tensioner that tensions a riser extending to the seabed from a drilling ship which drills for submarine resources such as oil.

2. Description of the Related Art

Currently, with rapid industrialization and development of technology, stable production and supply of resources such as oil has become a crucial global issue due to increase in use of such resources.

For this reason, development of marginal fields or deep-sea oilfields, which have been ignored due to their low economic feasibility, has become economically feasible. Thus, offshore drilling vessels suitable for seabed oilfields have been developed together with seabed drilling technology.

Conventionally, submarine drilling is performed using submarine drilling rig ships or stationary platforms, which can sail only with assistance of tugboats and are anchored at one point at sea using moorings during drilling operation. Recently, submarine drilling is performed using a drillship which is fitted with advanced drilling apparatuses and has the same shape as a general ship so as to sail by its own power.

A rig ship or drillship (hereinafter, referred to as a drilling ship) fitted with a variety of drilling apparatuses to drill for oil or gas under the seabed is formed at the center thereof with a moon pool through which a riser or a drill pipe can move vertically for drilling operation.

FIG. 1 is a side view of a conventional drilling ship floating on a sea surface for drilling operation.

A worker advances a riser 4 and a drill pipe 5 downwards through a moon pool 3 formed at the center of a drilling ship 1 using a lifting device provided to a derrick 2 to drill for submarine resources stored in an oil well 13 at bedrock 12 under the seabed 6.

The riser 4 is advanced to the seabed 6 to provide a path through which mud returns, prior to advancing the drill pipe 5 to the oil well 13. With the riser 4 installed between the drilling ship and the seabed, the drill pipe 5 is advanced downwards inside the riser 4 to the oil well 13 through a sea bottom stratum 11.

As such, when the riser 4 is advanced downwards to the seabed 6 or the drill pipe 5 is advanced to the oil well 13, short riser members of the riser or pipe members of the drill pipe 5 connected to each other are advanced downwards instead of using long riser members or drill pipe members connected to each other. On the seabed 6, a blowout preventer (BOP) 7 is installed to prevent high pressure from being transferred upwards along the drill pipe 5. In the sea bottom stratum 11, a casing 8 is secured by cement and a drill pipe 5 fitted with a drill bit 10 is inserted into the casing 8 to drill for submarine resources. To prevent the drill bit 10 from being excessively heated by heat generated by drilling operation of the drill bit 10 into the sea bottom stratum while facilitating the drilling operation through lubrication, mud 9 is inserted into the drill pipe 5. Then, the mud is discharged through the drill bit 10 and returns through the casing 8 and the riser 4. When drilling is completed, the drill pipe 5 is transferred to a drill floor through the moon pool 3, followed by disassembly for transportation to a storage location.

FIG. 2 is an enlarged view of Part A in FIG. 1.

The riser 4 may be divided into an upper riser 4 a and a lower riser 4 b with respect to a slip joint 20. Although the riser 4 extends from the drilling ship to the sea bottom, the slip joint 20 is provided to the middle of the riser 4 to allow the upper and lower risers 4 a, 4 b to move vertically with respect to each other in order to prevent vibration from being directly transferred from the upper riser 4 a connected to the drilling ship to the lower riser 4 b due to waves.

Since the distance of the riser 4 from the drilling ship to the sea bottom is several thousand meters and the mud passes through the riser 4, the total weight of the riser 4, the mud inside the riser and the BOP approaches several tons.

When the drilling ship is moved by waves and force generated due to movement of the upper riser 4 a connected to the drilling ship is directly transferred to the lower riser 4 b, the riser 4 having a length of several thousand meters may undergo buckling. To prevent such a phenomenon, the drilling ship is provided with the slip joint 20 and a riser tensioner. The riser tensioner tensions the lower riser 4 b with a predetermined tensile force, thereby minimizing influence of movement of the drilling ship by waves on the riser 4.

The riser tensioner generally includes a support ring 30, a cylinder device 40, and a hydraulic device 50.

The support ring 30 connects the slip joint 20 to the cylinder device 40. The cylinder device 40 includes a cylinder 41 connected to the drilling ship and a piston rod 42 connected to the support ring 30. Generally, a plurality of cylinder devices 40 is arranged along the circumference of the riser 4. The hydraulic device 50 supplies hydraulic pressure to each of the cylinders 41 to raise the piston rod 42, so that the lower riser 4 b connected to the slip joint 20 is tensioned.

The hydraulic device 50 includes an accumulator 51 and a pneumatic container 52. When air is supplied from the pneumatic container 52 to the accumulator 51, oil is supplied into the cylinder 41 by pressure of the air, thereby lifting the piston rod 42.

In the case where the distance between the cylinder 41 and the piston 42 is changed due to vertical movement of the drilling ship by waves, hydraulic pressure supplied to the cylinder 41 by the hydraulic device is controlled to be constant to pull the lower riser 4 b by constant tensile force.

Since the moon pool of the drilling ship is likely to form a cloud of spray when the waves lap against the drilling ship, the riser tensioner is always exposed to seawater. Thus, the piston rod 42 of the cylinder 41 contacts seawater and dries over time, so that salt accumulates on the surface of the piston rod 42. The salt enters the cylinder 41 by reciprocation of the piston rod 42.

As the riser tensioner is used for a long duration, the salt is accumulated on the riser tensioner and provides negative influence upon reciprocation of the piston rod 42. Therefore, there is a need for a device capable of removing salt from the piston rod 42.

A riser tensioner disclosed in US Patent Publication No. 2007/0056739 (publication date: Mar. 15, 2007) has difficulty in removal of foreign matter attached to a piston rod of the riser tensioner. Korean Utility Model Registration No. 20-0212631 (issue date: Feb. 15, 2001) discloses an air injection nozzle for removing foreign matter attached to a piston rod of an air cylinder. However, the injection nozzle cannot be used at sea and has low efficiency of removing foreign matter from the piston rod.

BRIEF SUMMARY

The present disclosure is directed to solving the problems of the related art as described above, and an embodiment of the present disclosure provides a riser tensioner which is provided with a mechanism capable of removing salt from a surface of a piston rod to prevent the salt from being accumulated on the surface of the piston rod exposed to seawater.

In accordance with one aspect of the present disclosure, there is provided a riser tensioner disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and including a plurality of cylinders. The riser tensioner further includes: an injection nozzle for injecting water to a surface of a piston rod to prevent salt from being accumulated on the surface of the piston rod exposed from each of the cylinders; and a scraper unit which removes salt or seawater from the surface of the piston rod by scrapping the surface of the piston rod to prevent salt from being accumulated on the surface of the piston rod.

The scraper unit may be operated immediately after the injection nozzle injects water.

The scraper unit may be provided to one end of the cylinder.

The scraper unit may include a scraper which is brought into close contact with the surface of the piston rod in operation and is separated from the surface of the piston rod during non-operation of the scraper unit.

As such, the riser tensioner according to the present disclosure includes the injection nozzle for injecting water to the surface of the piston rod and the scraper unit for removing seawater or salt from the surface of the piston rod by scrapping the surface of the piston rod, thereby preventing the salt from being accumulated on the surface of the piston rod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a conventional drilling ship floating on a sea surface for drilling operation;

FIG. 2 is an enlarged view of Part A in FIG. 1; and

FIG. 3 is a cross-sectional view of a riser tensioner in accordance with one embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Herein, like elements will be denoted by like reference numerals throughout the accompany drawings.

FIG. 3 is a cross-sectional view of a riser tensioner in accordance with one embodiment of the present disclosure.

Generally, a riser tensioner refers to a device that is connected to a drilling ship to tension a riser in order to prevent the riser from buckling upon movement of the drilling ship by waves during drilling for submarine resources.

A riser tensioner 100 according to one embodiment is also configured to tension the riser by allowing a piston rod 120 to be pulled by hydraulic pressure supplied to a cylinder 110.

The riser tensioner 100 includes an injection nozzle 130 configured to inject water to a surface of the piston rod 120 exposed from the cylinder 110 in order to prevent salt from being accumulated on the surface of the piston rod 120 and from entering the cylinder 110 upon reciprocation of the piston rod 120. That is, the injection nozzle 130 of the riser tensioner prevents negative influence of salt upon reciprocation of the piston rod 120, which can occur when salt enters the piston rod 120.

The injection nozzle 130 may be provided to one end of the cylinder 110. The injection nozzle 130 has injection ports 130 a, 130 b disposed to face the piston rod 120 such that water can be uniformly injected to the surface of the piston rod 120 through the injection ports 130 a, 130 b of the injection nozzle 130 to remove seawater or salt from the surface of the piston rod. The riser tensioner may include two or more injection nozzles 130 along the circumference of the piston rod 120. Further, each of the injection nozzles 130 may include a plurality of injection ports 130 a, 130 b longitudinally arranged along the piston rod 120.

Each of the injection nozzles 130 may be connected to a water supply system 131 to allow water to be injected at high pressure from the water supply system 131 towards the surface of the piston rod 120 through the injection nozzles 130. The water supply system 131 may be configured to allow water to be continuously or periodically injected through the injection nozzle 130. An interval for water injection, and the shape, number and position of the injection nozzles 130 may be suitably changed by those skilled in the art as needed.

The riser tensioner according to this embodiment may further include a scraper unit 140, 141 to remove seawater or salt from a surface of the piston rod by scraping the surface of the piston rod 120.

The scraper unit 140, 141 includes a scraper 140 brought into direct contact with the surface of the piston rod 120 to remove seawater or salt from the surface of the piston rod 120, and a controller 141 controlling the scraper 140.

The scraper 140 may be installed to one end of the cylinder 110 to be brought into contact with the surface of the piston rod 120 in operation and to be separated from the surface of the piston rod 120 during non-operation. In operation, the scraper 140 is driven by a driver (not shown) and linearly moves in a longitudinal direction along the surface of the piston rod 120 to return to an original position after removing the seawater or salt from the surface of the piston rod 120.

The scraper unit 140, 141 is operated to remove seawater or salt from the surface of the piston rod 120 immediately after the injection nozzles 130 injects water towards the surface of the piston rod. The shape and position of the scraper unit 140, 141 may be suitably changed by those skilled in the art as needed.

As described above, the riser tensioner 100 according to the embodiment includes the injection nozzles 130 for injecting water to the surface of the piston rod 120 exposed from the cylinder 110, and the scraper unit 140, 141 for removing seawater or salt from the surface of the piston rod 120 by scrapping the surface of the piston rod 120, thereby preventing the salt from being accumulated on the surface of the piston rod 120.

The riser tensioner according to the embodiment is provided to a drilling ship used for drilling of submarine resources. Here, the drilling ship means any kind of offshore floating structure for drilling of submarine resources, such as drill ships, rigs, semi-submersible rigs, tension leg platforms, and the like.

The embodiment described above can be combined to provide further embodiments. All of the patents, patent application publications, patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiment can be modified, if necessary, to employ concepts of the various patents, applications and publications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed as limiting the claims to the specific embodiments disclosed in the specification and the claims, but should be construed as including all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 

1. A riser tensioner disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and including a plurality of cylinders, the riser tensioner further comprising: an injection nozzle for injecting water to a surface of a piston rod to prevent salt from being accumulated on the surface of the piston rod exposed from each of the cylinders; and a scraper unit which removes salt or seawater from the surface of the piston rod by scrapping the surface of the piston rod to prevent salt from being accumulated on the surface of the piston rod.
 2. The riser tensioner of claim 1, wherein the scraper unit is operated immediately after the injection nozzle injects water.
 3. The riser tensioner of claim 1, wherein the scraper unit is provided to one end of the cylinder.
 4. The riser tensioner of claim 1, wherein the scraper unit comprises a scraper which is brought into close contact with the surface of the piston rod in operation and is separated from the surface of the piston rod during non-operation of the scraper unit. 